A 2012 Geely Free Cruiser sedan, with a mileage of 45,000 km, reports 1 cylinder misfire. Now the possibility of cylinder line, spark plug, ignition coil, and injector failure has been ruled out. What other problems can cause this failure? When the failure occurs, the ignition advance angle of cylinder 1 is 23°, which is about 7° when normal. Is there any problem?
Answer: The valve seal is not good or the piston ring is worn.